CD8 positive lymphocytes (T/CD8+) play an important role in host immunity to viruses . Anti-viral T/CD8+ recognize MHC class I molecules bound to peptides derived from a cytosolic pool of viral proteins. One of the curious features of T/CD8+ responses to viral infections is that it typically focuses on a highly limited set of peptides. This phenomenon, termed immunodominance, is crucial to understand if we are to develop vaccines that optimally elicit T/CD8+ responses. In this project we are investigating the various factors that contribute to immunodominance, including antigen processing, T cell regulation, and T cell receptor repertoire.